Melt butter in a saute pan. Meanwhile, in a separate bowl, beat eggs with a few teaspoonfuls of water.

Saute onion and asparagus until softened, about 5 minutes. Pour eggs over top and cook gently until set, all the while using a spatula to lift the edges of the omelette and let wet eggs slip underneath to cook.

When all wet egg has been moved under the omelette, gently flip the omelette and quickly cook the other side.